1. Field of the Invention
The present invention relates to a fuse box for use in a semiconductor device. More particularly, the invention relates to a fuse box for a semiconductor device having a bypass structure capable of reducing the number of cutting axes, and a method of forming same.
This application claims the benefit of Korean Patent Application No. 10-2006-0076372, filed on Aug. 11, 2006, the subject matter of which is hereby incorporated by reference.
2. Description of the Related Art
With dramatically increased integration density, the possibility of defective memory cells within contemporary semiconductor memory devices increases. Production yield for such semiconductor devices will decrease in the absence of remedy for defective memory cells. Therefore, a number of different repair methods and mechanisms have been proposed, including various redundancy circuits.
Some of these repair methods essentially replace a defective memory cell within its constituent array of memory cells. That is, once a defective memory cell has been identified through routine testing, it may be replaced by a memory cell in a redundancy circuit. The physical removal of the defective memory cell and its replacement with a redundancy cell may be accomplished through the use of fuses contained in a fuse box. Fuse box circuits are commonly provided within the context of certain repair methods in the peripheral circuit region of the semiconductor memory device. By selectively “cutting” fuses in the fuse box the replacement of a defective memory cell may be accomplished.
FIG. 1A is a plan view illustrating a fuse box 10 used to repair a defective memory cell in a conventional semiconductor device. Fuse box 10 comprises an arrangement of fuses 15 separated by a predetermined fuse pitch “P”. To facilitate cutting by a laser, each fuse 15 is exposed through a fuse opening region 13. The fuse 15 may be cut by irradiating it with a laser beam 17 having a predetermined diameter, (or spot size) “S”. Thus, a normally conductive fuse 15 may be placed in a non-conductive state by cutting it with laser beam 17.
Each fuse 15 is formed as a trace having a predetermined width “W”. Adjacent fuses 15 are separated by fuse pitch P. The width W of fuse 15 is sized relative to the spot size of laser beam 17 so as to absorb the laser energy. Further, the fuse pitch P is preferably greater than a deviation range for the positioning accuracy “A” of laser beam 17.
Unfortunately, as the integration density of contemporary semiconductor memory devices increases, the number of fuses associated with various repair methods and mechanisms also increases. All things being equal, this increased number of fuses results in a reduction in the fuse pitch P separating adjacent fuses and/or a reduction in the width W of each fuse. Accordingly, fuses run the risk of being damaged during the cutting of an adjacent fuse.
To reduce this risk of damage to adjacent fuses, an improved conventional fuse box has been proposed. This fuse box contains fuses having a relatively large fuse pitch in a fuse opening region. In the fuse box, the fuses are arranged such that a first relatively large fuse pitch in the fuse opening region is greater than the deviation range of the positioning accuracy of an applied laser. A second relatively narrow fuse pitch is used outside the fuse opening region so that the fuses may be arranged in a bundle. The fuse opening region is a region specifically designed to facilitate effective fuse cutting (i.e., expose the plurality of fuses to a cutting laser). Outside the fuse opening region fuse cutting is not performed and the fuses need not be exposed.
In the improved conventional fuse box, since the fuses are arranged with a relatively large first fuse pitch in the fuse opening region, fuse cutting can be easily performed without risk of damage to adjacent fuses. However, the closely bundled fuses outside the fuse opening region are still susceptible to melting caused by the heat of near-by fuse cutting. FIG. 1B is an actual image of a bridge 19 shorting two adjacent fuses. Bridge 19 was caused by melted fuse metal from proximate heating due to fuse cutting.
Additionally, in the improved conventional fuse box, the arrangement of fuses assumes a plurality of cutting axes. The provision of numerous fuse cutting axes facilitates an increase in the first fuse pitch in the fuse opening region. Unfortunately, it also increases the positioning time for the laser beam within the fuse opening region. This increased positioning time slows down the process of fuse cutting. Therefore, the number of the cutting axes should be reduced in order to improve a throughput of semiconductor memory devices in a fuse cutting process.